feat(aether-proxy): 网络层全面优化与代理耗时追踪

aether-proxy:
- 新增 20+ 可配置参数：Aether API/delegate/CONNECT 各阶段超时、连接池、TCP keepalive/nodelay
- AetherClient 支持指数退避重试(可配置次数/延迟)和 HTTP/2
- 新增 DNS 缓存(TTL + 容量限制)避免重复解析
- 新增并发连接数限制(Semaphore，默认基于硬件估算)
- CONNECT 隧道增加建连超时和升级超时
- TLS 增加握手超时、会话缓存(session ticket + memory cache)、ALPN 协商
- 新增 ProxyMetrics 收集请求计数和延迟，通过心跳上报
- delegate 响应注入 X-Proxy-Timing 头(dns_ms/upstream_ms/total_ms)

后端:
- StreamContext 和 handler 提取 X-Proxy-Timing 写入 proxy_info 追踪数据

前端:
- 请求时间线展示代理分阶段耗时(DNS/上游)
- Endpoint 添加按钮改为文字按钮样式

aether-proxy/Cargo.toml

@@ -9,7 +9,7 @@ tokio = { version = "1", features = ["full"] }
 hyper = { version = "1", features = ["http1", "server"] }
 hyper-util = { version = "0.1", features = ["tokio", "http1", "server"] }
 http-body-util = "0.1"
-reqwest = { version = "0.12", default-features = false, features = ["json", "rustls-tls", "stream"] }
+reqwest = { version = "0.12", default-features = false, features = ["json", "rustls-tls", "stream", "http2"] }
 futures-util = "0.3"
 hmac = "0.12"
 sha2 = "0.10"